Specific Localization of the Gap Junctional Protein Connexin 32 in Equine Gastric Mucosa

Gap junctional inter-cellular communication (GJIC) is known to be important in the maintenance of tissue homeostasis. Evidence is accumulating that GJIC plays an important role in the gastric mucosal defence system and that the loss of GJIC is associated with gastric ulcer formation. The prevalence of gastric ulceration in foals and horses is high. However, there are no studies about the presence of gap junctions in gastric mucosa of horses. The purpose of this study was to investigate the distribution pattern of the gap junction protein 32 in normal gastric mucosa of horses. Immunocytochemical observations were made with light microscopy on cryosections of fresh frozen gastric mucosa from the fundic region, pyloric region, margo plicatus and pars nonglandularis. Immunohistochemical staining was performed by standard immunoperoxidase techniques using an anti-connexin 32 polyclonal antibody. In Situ Hybridization, Western Blot Analysis and RT-PCR were performed to confirm the presence of connexin 32. In normal horse gastric mucosa, connexin 32 was abundant in the surface epithelium and in a decreasing staining gradient extending down to the neck of the glands. Gastric surface mucous cells are formed in the neck of the glands and migrate along the foveola toward the mucosal surface. So, immature forms of surface mucous cells are found in the generative zone and in the deep part of the foveola, whereas well-matured ones cover the upper part of the foveola and the luminal surface of the mucosa. Therefore, these findings are in line with other studies, which described larger and more numerous gap junctions in mature surface mucous cells than in immature cells. These results show that gap junctions develop during the maturation of surface mucous cells and suggest that GJIC between gastric surface mucous cells plays an important role in the regulation of cell differentiation and in tissue homeostasis. Further studies are required to investigate the distribution pattern of connexin 32 in the gastric mucosa of horses with gastric ulcer.